A wireless multihop communications network, such as a mesh network, includes a set of node devices capable of exchanging messages with one another over a wireless medium, typically using radio frequency (RF) airwaves. Each of the node devices can be primarily a communications device or, alternatively, the communications functionality may be secondary to its primary function. For example, in a given node, the communications circuitry can be a part of a device such as a computer system, a smart appliance, a vehicle, a media device, a piece of industrial equipment (e.g., an instrument, machine, sensor, actuator), and the like. In a mesh architecture the node devices are uniquely addressable, and able to route messages from an originating node device toward the intended destination node. In general, each of the node devices can be an originating and destination node device as well. Thus, node devices perform both, message forwarding, and message origination/consumption functions. This means that the communication channels can be quite busy at certain parts of the network where node density is high and the message density is relatively higher than at other parts.
Wireless networks in particular face other challenges. For instance, wireless links may not always be reliable: there may be intermittent interfering signals, intermittent obstructions, including large movable objects (e.g., vehicles) moving in and out of the transmission path, weather affecting the quality of radio signal propagation, etc., affecting the signal strength of transmissions seen by the receiving node. Also, certain node devices may be situated near the limits of their radio's communication range, which further compounds signal reception challenges.
For node devices in wireless mesh networks, having multiple neighboring node devices through which communications can be sent and received is advantageous in several respects. In general, having a higher number of neighbors is better in terms of increasing coverage and providing an ability to select higher-quality communications paths. A higher count of neighbors also provides robustness and self-healing capability in the mesh network by supporting a diversity of alternative communications paths.
In a wireless mesh network with very high neighbor density, it is possible to have hundreds or even thousands of neighboring node devices within communication range of one another. This situation can come into play particularly when node devices are able to transmit at high power levels, thereby reaching more distant node devices. In spite of the advantages of having multiple neighbors, there is an important trade-off: maintaining a high number of neighbors is costly in terms of memory and processing capacity needed in each of the node devices. These added costs can be significant particularly for node devices deigned to be low-cost.
Maintaining neighbors typically involves establishing periodic communications between devices and re-evaluating the links to each neighbor in order to coordinate network routing and communicating functions. Specific information is gathered and exchanged between individual sets of neighboring devices to allow network connectivity and route optimizing decisions to be made. Therefore, the greater the density of deployed devices, in terms of number of visible radio neighbors in a given geographic area, the greater is the system overhead that may be associated with the communications and data exchanges that occurs among neighbors.
If not properly controlled, communicating with a large number of neighbors can take up a significant portion of the available communications capacity in the network neighborhood, which can degrade overall radio link performance. Increased communications in high-density networks, even those due to messages for neighbor management, result in an increased rate at which messages “collide”—i.e., interfere with one another, preventing reception of one or more of the transmitted messages. Communications received with errors detected therein must be re-transmitted, which uses additional communication overhead in the system, thereby further aggravating the problem.
A solution is therefore needed that improves the communications performance in high-density wireless mesh networks.